Message ID | 1518555259-26463-1-git-send-email-rbraun@sceen.net |
---|---|
State | New |
Headers | show |
Series | [v2] hw/char/stm32f2xx_usart: fix TXE/TC bit handling | expand |
On Tue, Feb 13, 2018 at 12:54 PM, Richard Braun <rbraun@sceen.net> wrote: > I/O currently being synchronous, there is no reason to ever clear the > SR_TXE bit. However the SR_TC bit may be cleared by software writing > to the SR register, so set it on each write. > > In addition, fix the reset value of the USART status register. > > Signed-off-by: Richard Braun <rbraun@sceen.net> Reviewed-by: Alistair Francis <alistair.francis@xilinx.com> Alistair > --- > hw/char/stm32f2xx_usart.c | 12 ++++++++---- > include/hw/char/stm32f2xx_usart.h | 7 ++++++- > 2 files changed, 14 insertions(+), 5 deletions(-) > > diff --git a/hw/char/stm32f2xx_usart.c b/hw/char/stm32f2xx_usart.c > index 07b462d4b6..032b5fda13 100644 > --- a/hw/char/stm32f2xx_usart.c > +++ b/hw/char/stm32f2xx_usart.c > @@ -96,12 +96,10 @@ static uint64_t stm32f2xx_usart_read(void *opaque, hwaddr addr, > switch (addr) { > case USART_SR: > retvalue = s->usart_sr; > - s->usart_sr &= ~USART_SR_TC; > qemu_chr_fe_accept_input(&s->chr); > return retvalue; > case USART_DR: > DB_PRINT("Value: 0x%" PRIx32 ", %c\n", s->usart_dr, (char) s->usart_dr); > - s->usart_sr |= USART_SR_TXE; > s->usart_sr &= ~USART_SR_RXNE; > qemu_chr_fe_accept_input(&s->chr); > qemu_set_irq(s->irq, 0); > @@ -137,7 +135,9 @@ static void stm32f2xx_usart_write(void *opaque, hwaddr addr, > switch (addr) { > case USART_SR: > if (value <= 0x3FF) { > - s->usart_sr = value; > + /* I/O being synchronous, TXE is always set. In addition, it may > + only be set by hardware, so keep it set here. */ > + s->usart_sr = value | USART_SR_TXE; > } else { > s->usart_sr &= value; > } > @@ -151,8 +151,12 @@ static void stm32f2xx_usart_write(void *opaque, hwaddr addr, > /* XXX this blocks entire thread. Rewrite to use > * qemu_chr_fe_write and background I/O callbacks */ > qemu_chr_fe_write_all(&s->chr, &ch, 1); > + /* XXX I/O are currently synchronous, making it impossible for > + software to observe transient states where TXE or TC aren't > + set. Unlike TXE however, which is read-only, software may > + clear TC by writing 0 to the SR register, so set it again > + on each write. */ > s->usart_sr |= USART_SR_TC; > - s->usart_sr &= ~USART_SR_TXE; > } > return; > case USART_BRR: > diff --git a/include/hw/char/stm32f2xx_usart.h b/include/hw/char/stm32f2xx_usart.h > index 9d03a7527c..7ea7448813 100644 > --- a/include/hw/char/stm32f2xx_usart.h > +++ b/include/hw/char/stm32f2xx_usart.h > @@ -37,7 +37,12 @@ > #define USART_CR3 0x14 > #define USART_GTPR 0x18 > > -#define USART_SR_RESET 0x00C00000 > +/* > + * XXX The reset value mentioned in "24.6.1 Status register" seems bogus. > + * Looking at "Table 98 USART register map and reset values", it seems it > + * should be 0xc0, and that's how real hardware behaves. > + */ > +#define USART_SR_RESET (USART_SR_TXE | USART_SR_TC) > > #define USART_SR_TXE (1 << 7) > #define USART_SR_TC (1 << 6) > -- > 2.11.0 > >
On 15 February 2018 at 22:27, Alistair Francis <alistair23@gmail.com> wrote: > On Tue, Feb 13, 2018 at 12:54 PM, Richard Braun <rbraun@sceen.net> wrote: >> I/O currently being synchronous, there is no reason to ever clear the >> SR_TXE bit. However the SR_TC bit may be cleared by software writing >> to the SR register, so set it on each write. >> >> In addition, fix the reset value of the USART status register. >> >> Signed-off-by: Richard Braun <rbraun@sceen.net> > > Reviewed-by: Alistair Francis <alistair.francis@xilinx.com> Applied to target-arm.next, thanks. -- PMM
diff --git a/hw/char/stm32f2xx_usart.c b/hw/char/stm32f2xx_usart.c index 07b462d4b6..032b5fda13 100644 --- a/hw/char/stm32f2xx_usart.c +++ b/hw/char/stm32f2xx_usart.c @@ -96,12 +96,10 @@ static uint64_t stm32f2xx_usart_read(void *opaque, hwaddr addr, switch (addr) { case USART_SR: retvalue = s->usart_sr; - s->usart_sr &= ~USART_SR_TC; qemu_chr_fe_accept_input(&s->chr); return retvalue; case USART_DR: DB_PRINT("Value: 0x%" PRIx32 ", %c\n", s->usart_dr, (char) s->usart_dr); - s->usart_sr |= USART_SR_TXE; s->usart_sr &= ~USART_SR_RXNE; qemu_chr_fe_accept_input(&s->chr); qemu_set_irq(s->irq, 0); @@ -137,7 +135,9 @@ static void stm32f2xx_usart_write(void *opaque, hwaddr addr, switch (addr) { case USART_SR: if (value <= 0x3FF) { - s->usart_sr = value; + /* I/O being synchronous, TXE is always set. In addition, it may + only be set by hardware, so keep it set here. */ + s->usart_sr = value | USART_SR_TXE; } else { s->usart_sr &= value; } @@ -151,8 +151,12 @@ static void stm32f2xx_usart_write(void *opaque, hwaddr addr, /* XXX this blocks entire thread. Rewrite to use * qemu_chr_fe_write and background I/O callbacks */ qemu_chr_fe_write_all(&s->chr, &ch, 1); + /* XXX I/O are currently synchronous, making it impossible for + software to observe transient states where TXE or TC aren't + set. Unlike TXE however, which is read-only, software may + clear TC by writing 0 to the SR register, so set it again + on each write. */ s->usart_sr |= USART_SR_TC; - s->usart_sr &= ~USART_SR_TXE; } return; case USART_BRR: diff --git a/include/hw/char/stm32f2xx_usart.h b/include/hw/char/stm32f2xx_usart.h index 9d03a7527c..7ea7448813 100644 --- a/include/hw/char/stm32f2xx_usart.h +++ b/include/hw/char/stm32f2xx_usart.h @@ -37,7 +37,12 @@ #define USART_CR3 0x14 #define USART_GTPR 0x18 -#define USART_SR_RESET 0x00C00000 +/* + * XXX The reset value mentioned in "24.6.1 Status register" seems bogus. + * Looking at "Table 98 USART register map and reset values", it seems it + * should be 0xc0, and that's how real hardware behaves. + */ +#define USART_SR_RESET (USART_SR_TXE | USART_SR_TC) #define USART_SR_TXE (1 << 7) #define USART_SR_TC (1 << 6)
I/O currently being synchronous, there is no reason to ever clear the SR_TXE bit. However the SR_TC bit may be cleared by software writing to the SR register, so set it on each write. In addition, fix the reset value of the USART status register. Signed-off-by: Richard Braun <rbraun@sceen.net> --- hw/char/stm32f2xx_usart.c | 12 ++++++++---- include/hw/char/stm32f2xx_usart.h | 7 ++++++- 2 files changed, 14 insertions(+), 5 deletions(-)